1. Database System Concepts and Architecture
Chapter 2
Database System Concepts and Architecture

2. Database System Concepts and Architecture
Basic client/server DBMS architecture
Client module
Server module

3. Data Models, Schemas, and Instances (cont'd.)
Collection of concepts that describe the structure of a database
Provides means to achieve data abstraction
Basic operations
Specify retrievals and updates on the database
Dynamic aspect or behavior of a database application
Allows the database designer to specify a set of valid operations allowed on database objects

4. Categories of Data Models
High-level or conceptual data models
Close to the way many users perceive data
Low-level or physical data models
Describe the details of how data is stored on computer storage media
Representational data models
Easily understood by end users
Also similar to how data organized in computer storage

5. Categories of Data Models (cont'd.)
Entity
Represents a real-world object or concept
Attribute
Represents some property of interest
Further describes an entity
Relationship among two or more entities
Represents an association among the entities
Entity-Relationship model

6. Categories of Data Models (cont'd.)
Relational data model
Used most frequently in traditional commercial DBMSs
Object data model
New family of higher-level implementation data models
Closer to conceptual data models

7. Categories of Data Models (cont'd.)
Physical data models
Describe how data is stored as files in the computer
Access path
Structure that makes the search for particular database records efficient
Index
Example of an access path
Allows direct access to data using an index term or a keyword

8. Schemas, Instances, and Database State
Database schema
Description of a database
Schema diagram
Displays selected aspects of schema
Schema construct
Each object in the schema
Database state or snapshot
Data in database at a particular moment in time

9. Schemas, Instances, and Database State (cont'd.)

10. Example of a database state

11. Schemas, Instances, and Database State (cont'd.)
Define a new database
Specify database schema to the DBMS
Initial state
Populated or loaded with the initial data
Valid state
Satisfies the structure and constraints specified in the schema

12. Schemas, Instances, and Database State (cont'd.)
Schema evolution
Changes applied to schema as application requirements change

13. Database Schema vs. Database State (continued)
Distinction
The database schema changes very infrequently.
The database state changes every time the database is updated.
Schema is also called intension.
State is also called extension.

14. DBMS Languages Data definition language (DDL)
Defines both schemas
Data manipulation language (DML)
Allows retrieval, insertion, deletion, modification

15. The Database System Environment
DBMS component modules
Buffer management
Stored data manager
DDL compiler
Interactive query interface
Query compiler
Query optimizer
Precompiler

16. The Database System Environment (cont'd.)
DBMS component modules
Runtime database processor
System catalog
Concurrency control system
Backup and recovery system

17. Database System Utilities
Loading
Load existing data files
Backup
Creates a backup copy of the database

18. Database System Utilities (cont'd.)
Database storage reorganization
Reorganize a set of database files into different file organizations
Performance monitoring
Monitors database usage and provides statistics to the DBA

19. Tools, Application Environments, and Communications Facilities
CASE Tools
Data dictionary (data repository) system
Stores design decisions, usage standards, application program descriptions, and user information
Application development environments
Communications software

20. Centralized and Client/Server Architectures for DBMSs
Centralized DBMSs Architecture
All DBMS functionality, application program execution, and user interface processing carried out on one machine

21. Basic Client/Server Architectures
Servers with specific functionalities
File server
Maintains the files of the client machines.
Printer server
Connected to various printers; all print requests by the clients are forwarded to this machine
Web servers or servers

22. Basic Client/Server Architectures (cont'd.)
Client machines
Provide user with:
Appropriate interfaces to utilize these servers
Local processing power to run local applications

24. Basic Client/Server Architectures (cont'd.)
User machine that provides user interface capabilities and local processing
Server
System containing both hardware and software
Provides services to the client machines
Such as file access, printing, archiving, or database access

25. Two-Tier Client/Server Architectures for DBMSs
Server handles
Query and transaction functionality related to SQL processing
Client handles
User interface programs and application programs

26. Three-Tier and n-Tier Architectures for Web Applications
Application server or Web server
Adds intermediate layer between client and the database server
Runs application programs and stores business rules
N-tier
Divide the layers between the user and the stored data further into finer components